Don,
Base oil viscosity is the most important property of a grease. After all it is a lubricant and same rules apply that film thickness is a result of viscosity.
The choice of viscosity is a balance between bearing contact friction and fluid film friction meaning that if the viscosity is too low it will produce frictional heat and excessive wear and if it is too high it will also produce frictional heat, energy losses and shorten lubricant life. At slow peripheral speeds the impact on bearing life and bearing replacement cost exceed the cost for energy losses but at normal to higher speeds the cost of the energy losses can significantly exceed the bearing replacement cost.
Management and procurement always want to simplify and reduce SKU's but the cost of doing so can sometimes be very high. The energy consumption due to power losses could increase beyond your immagination or the bearing life and bearing replacement cost could increase. In addition lubrication interval, labor costs, lubricant consumption and waste handling costs could be affected.
When going through a porfolio harmonization like that you need expert help to ensure that you don't make any critical misstakes that would end up on someone elses budget.
This is the kind of stuff i've been doing for a living for the past 25 yrs.
Cheers,
GG